1. Field of the Invention
The present invention relates to an exposure apparatus with which, in general, a fine circuit pattern is transferred and, more particularly, to an exposure apparatus having piping made of a high polymer material (i.e., piping made of resin) and arranged inside the exposure apparatus.
2. Description of the Related Art
Hitherto, as a printing method (e.g., photolithography) for forming fine semiconductor elements such as semiconductor memories, logic circuits or the like, reduction projection exposure has been employed. The minimum size of an object which can be transferred by the reduction projection exposure is proportional to the wavelength of light used for the transfer, and is inversely proportional to the numerical aperture of the projection optical system. Therefore, light beams having shorter wavelengths have been applied to transfer finer circuit patterns. In particular, ultra-violet (UV) rays having shorter wavelengths have been employed. That is, mercury lamp i rays (365 nm in wavelength), KrF excimer laser beams (248 nm), and ArF excimer laser beams (193 nm) have been used. At present, an exposure apparatus using UV rays having a still shorter wavelength, i.e., F2 laser beams (157 mm) is under development. In the wavelength range of the F2 laser, the absorption of the beams into oxygen is not negligible. Thus, an exposure apparatus using the F2 laser has a structure in which an inert gas such as nitrogen, helium, or the like can be filled in the spaces through which the light beams travel.
For efficient printing of very fine circuit patterns with a size of less than 0.1 μm, a reduction projection exposure apparatus using extreme UV (EUV) rays having a still shorter wavelength than UV rays, i.e., having a wavelength of about 10 to 15 nm, has been developed. Moreover, an exposure apparatus using an electron beam (EB) has been developed. Referring to exposure apparatuses using electron beams, different types of exposure apparatuses, e.g., a direct-writing system, a multiple-electron-source system, a stencil mask system, and the like, have been developed. For the above-described exposure apparatuses using EUV rays and EB, it is necessary to set the light-path space in a high vacuum state or in a reduced pressure environment.
However, when light beams having short wavelength are used for exposure, the light energy is increased, so that the light beams decompose slight amounts of carbon compounds which have been gasified and are present in the light paths. In some cases, due to the light energy, substances produced by the decomposition are deposited on and adhere to optical elements such as lenses, mirrors, stops and the like which constitute the exposure apparatus. Thus, in the case in which the optical elements are lenses, the transmittance is reduced. In the case in which the optical elements are mirrors, the reflectivity becomes low. In the case in which the optical elements are stops, the sizes and shapes are changed. Hence, the performances of the optical elements are deteriorated when substances produced by the decomposition adhere to the optical elements. When the respective optical elements are deteriorated, the radiation intensity (i.e., optical strength) or imaging-performance of the exposure apparatus is changed. Thus, the optical performance required of the exposure apparatus is deteriorated. In order to overcome the problem of deteriorated optical performance, a significant amount of labor and time is required to disassemble and clean the optical system. Therefore, countermeasures against the above described problems have been investigated. For example, it has been considered to fill the optical path space (i.e., exposure space) with a high-purity inert gas that does not decompose with light, or to keep the optical path space in a high vacuum state.
Present-day exposure apparatuses are provided with parts made of resins containing carbon compounds which may be deposited on and adhere to optical elements, deteriorating the performance of the exposure apparatuses. It is not practical to form exposure apparatuses which exclude resin parts. For example, when a wafer and a reticle are scanned and exposed, stages for moving the wafer and reticle are driven in the X-, Y-, and Z-axial directions and, moreover, the stages are driven rotationally. If the temperature of the wafer or reticle placed on the stage cannot be kept constant and uniform, deterioration of the transfer accuracy will occur. When the stage is driven, heat is generated in the driving members. Thus, waste-heat from the driving members must be taken into account. Ordinarily, in such cases, constant temperature water is circulated to eliminate the heat. To circulate constant temperature water through a stage which is repeatedly moved, a flexible resin-tube must be used.
It has been proposed to use a flexible metallic tube. However, with repeated movement, the metal may become fatigued. Thus, it would become necessary to frequently replace the metallic tubes. On the other hand, resin tubes are sufficiently durable for the repeated movement, and thus, are superior in safety and economy. However, the resin tubes are made of high polymer compounds, so that components of the high polymer compounds may be decomposed and gasified, although the amounts are slight, resulting in the above described problems.
At present, the development of a material for the tubes, such as fluorine-containing resins, from which a smaller amount of organic substance is released compared to known polyurethane tubes or the like has been investigated. However, in contrast to the emission of gas from an inorganic material, the emission of gas from an organic component is not negligible.
Japanese Patent Laid-Open No. 2001-297967 (corresponding U.S. Patent Publication Number 2002000029) discloses an exposure apparatus with which the amount of a gas component emitted from a resin tube can be reduced, even if the resin tube is arranged in a vacuum environment, as described with respect to the above-described exposure apparatuses using EUV rays and electron beams. Japanese Patent Laid-Open No. 2001-297967 discloses an exposure apparatus provided with a double piping composed of an inside piping made of resin and an outside piping also made of resin, that covers the outside periphery of the inside piping. A gas-exhausting mechanism for exhausting gas present in the space defined by the inside and outside pipings is also provided.
However, the invention disclosed in Japanese Patent Laid-Open No. 2001-297967 does not address the cases where it is necessary to further enhance the purity of an inert gas filled in the exposure space and the optical path space, to further enhance the vacuum (i.e., to decrease the atmospheric pressure), and to further reduce the concentration of gas which becomes a material deposited on and adhering to the optical elements (i.e., causing the contamination).